I undertake mystery shopping assignments from a number of companies. Their payments to me are often split into two - one part for reimbursement and one part for fee. The reimbursement will be for something I have to purchase - eg a cup of coffee, a purchase in a shop, entrance to an exhibition. These are not necessarily things I would usually buy and I usually go out specifically to undertake the assignment. Are the costs of these items allowable as a business expense in this situation?